1. Field of the Invention
This invention relates to the recovery of hydrocarbons in situ and, more particularly, to the recovery of hydrocarbons in situ by thermal extraction of hydrocarbon-containing subterranean formations, in conjunction with the recovery of heat from the extracted hydrocarbons.
2. Description of the Prior Art
Large deposits of coal and oil in the form of oil shale are found in various sections of the United States, particularly in Colorado and surrounding states and Canada. Various methods of gasifying the coal and recovering the oil from these shale deposits have been proposed. However, the principal difficulty with these methods is their high cost which renders the recovered products too expensive to compete with hydrocarbon gases and petroleum crudes recovered by more convention methods. For example, mining the coal or oil shale and removing the hydrocarbon therefrom by above-ground retorting in furnaces presents disposal and pollution problems, and also requires the use of extremely large quantities of coolant to reduce the temperature of the recovered products so that they can be marketed. Similarly, in situ retorting of the coal or oil shale to recover the hydrocarbons contained therein is made difficult because of the nonpermeable nature of the coal and oil shale and because of the massive amount of heat necessary to recover the hydrocarbon products. Nonetheless, the art discloses various means for improving the hydrocarbon recovery in situ from coal and oil shale such as described in U.S. Pat. Nos. 3,001,776 or 3,273,649 or 3,349,848 or 3,481,398. Although these references are directed to advancements of the art, they generally require rubblization techniques such as by means of explosive devices, e.g., nuclear energy, as well as the use of massive amounts of coolant and expensive heat exchange facilities.